1. Field of the Invention
The present invention relates to a motorized vehicle having left and right driving wheels independently driven by left and right electric motors, respectively.
2. Background Information
The term xe2x80x9cworking machinexe2x80x9d is used herein in a comprehensive sense, i.e., to broadly refer to a load-carrying vehicle, a tiller, a tractor, a lawn mower, a snowplow and so on. In case of the tiller, uncultivated areas are formed at ends of an arable land where the tiller makes a 180xc2x0 turn. The uncultivated areas should preferably be as small as possible. To meet this condition, the tiller is designed to have a smaller turning radius and, ideally, the tiller can make a turn while staying at the same position. Such a turn is referred to as xe2x80x9cspot turnxe2x80x9d. The spot turn is very useful not only for the tiller but also for other sorts of working machines because they are required to make sharp or abrupt turns frequently to avoid interference with obstacles.
Conventional techniques proposed to improve turning performance characteristics of working vehicles are disclosed in Japanese Patent Laid-open Publications Nos. 10-95360 and 6-87340
The working vehicle disclosed in Japanese Patent Laid-open Publications Nos. 10-95360 includes a travel HST continuously variable shift mechanism and a turning HST continuously variable shift mechanism disposed in juxtaposition. The travel UST continuously variable shift mechanism is operated by a speed change lever while the turning HST continuously variable shift mechanism is operated a round-type steering handle. The disclosed working vehicle is complicated in construction because a number of links are disposed in a complicated manner below the steering handle and speed change lever. Furthermore, the side-by-side arrangement of two shift mechanisms increases the number of components of the working vehicle and makes the working vehicle expensive to manufacture.
The working machine disclosed in Japanese Patent Laid-open Publications No. 6-87340 includes a hydraulic continuous variable transmission mechanism equipped with left and right neutral valves adapted to be operated by left and right side clutch control levers provided on left and right handlebars, respectively, of the working vehicle. When the left side clutch control lever is gripped together with the left handlebar, the left neutral valve is activated to realize a clutch-off state of the continuous variable transmission mechanism. Similarly, when the right side clutch control lever is gripped together with the right handlebar, the right neutral valve is activated to realize the clutch-off state of the continuous variable transmission mechanism. With this construction, when a spot turn is to be made, the operator is required to manipulate left and right side clutch control levers with high dexterity. A similar attempt by a non-skilled operator would result in a turn of the working vehicle achieved with an increased turning radius much larger than that attained by the spot turn.
It is accordingly an object of the present invention to provide a motorized vehicle which is simple in construction but can achieve a spot turn easily and reliably.
To achieve the foregoing object, according to the present invention, there is provided a motorized vehicle comprising: a vehicle body; a left driving wheel and a right driving wheel that are rotatably mounted on the vehicle body; a left electric motor and a right electric motor that are mounted on the vehicle body for independently rotating the left and right driving wheels, respectively, at variable speeds; and an actuator for causing one of the left and right electric motors to rotate in one direction and, at the same time, causing the other of the left and right electric motors to rotate in the opposite direction, thereby ensuring that the vehicle making a turn while staying at the same position.
In one preferred form, the motorized vehicle further includes a pair of left and right handlebars extending from the vehicle body in a rearward direction of the motorized vehicle, each of the handlebars having a handgrip adapted to be gripped by the operator. The actuator comprises a left brake and a right brake that are mounted on the vehicle body for independently applying brake forces to the left and right driving wheels, respectively, and a pair of left and right turn control levers pivotally mounted to the left and right handlebars, respectively, so as to extend along the corresponding handgrips. The left and right turn control levers are operatively connected to both the left and right brakes and the left and right electric motors, respectively, such that the left and right electric motors are caused to rotate simultaneously in opposite directions based on the angular positions of the left and right turn control levers. The left and right brakes are associated with the left and right electric motors, respectively, and separately apply the brake forces to the left and right driving wheels via the left and right electric motors.
It is preferable that the left and right turn control levers are angularly movable between an initial zero-brake position and a stroke end position opposite to the zero-brake position across a full-brake position. The left and right turn control levers are operatively linked with the left and right brakes and the left and right electric motors such that when the left turn control lever moves within a first range defined between the zero-brake position and the full-brake position, the brake force applied from the left brake varies linearly with the amount of displacement of the left turn control lever, when the left turn control lever moves within a second range defined between the full-brake position and the stroke end position, the left electric motor is rotated in the reverse direction, and the right electric motor is rotated in the forward direction, when the right turn control lever moves within the first range, the brake force applied from the right brake varies linearly with the amount of displacement of the right turn control lever, and when the right turn control lever moves within the second range, the right electric motor is rotated in the reverse direction, and the left electric motor is rotated in the forward direction.
In another preferred form, the actuator comprises a left spot turn switch operatively connected to the left and right electric motors and manually operable to cause the left electric motor to rotate in the reverse direction and the right electric motor to rotate in the forward direction, and a right spot turn switch operatively connected to the left and right electric motors and manually operable to cause the right electric motor to rotate in the reverse direction and the left electric motor to rotate in the forward direction. The motorized vehicle may further include an operator control panel mounted to the vehicle body in which instance, the left and right spot turn switches are provided on the operator control panel.
The motorized vehicle may further include a pair of left and right crawler belts driven by the left and right driving wheels.